This invention relates to the separation of higher molecular weight components from lower molecular weight components in a fluid stream. In a specific embodiment, it relates to the separation of the ethane or propane and higher molecular weight components from a natural gas stream containing methane.
Natural gas as it comes from the ground generally is not suitable for use directly without some processing. The basic processing operations carried out in a natural gas plant are to first remove acid gases such as CO.sub.2 and H.sub.2 S and then to pass the gas through a dehydration means to remove water. The resulting product can then be used as a fuel. However, such streams generally contain a substantial amount of higher molecular weight components such as ethane, propane and, to a lesser extent, butanes, and higher components. The heavier components are of greater value as chemical feedstocks than they are as a fuel. Consequently, it is desirable to separate either all of the heavier components from the methane or else separate propane and heavier from the methane and ethane.
It has long been known to separate ethane and higher components from methane by the use of an expander wherein a natural gas feed stream is passed to a high pressure separator and the vapor taken off and passed to an expander with the resulting vapor going to the upper portion of a stripper such as a demethanizerand the liquid from the separator going to the lower portion of the stripper. Such a system is not as efficient as would be desired, however.